Endocavitary Ultrasound Applicator for Hyperthermia Treatment of Cervical Cancer

摘要

An endocavitary ultrasound applicator has been developed for targeted heat delivery to the cervix. The device has multiple sectored tubular transducers for truly 3-D heating control (angular and along the length) and is integrated with an intracavitary HDR brachytherapy applicator for sequential administration of conformal heat and radiation. Brachytherapy treatment planning data are inspected to determine target thermal treatment volumes. Heat treatments are simulated with an acoustic and biothermal model of cervical tissue. Power control to individual elements and sectors is implemented for global maximum and pilot point control to limit rectum and bladder temperature. A parametric analysis of device parameters, tissue properties, and catheter materials is conducted to assess their effects on heating patterns and inform device development. Acoustic output of all devices was characterized. MR thermal imaging is used to analyze 3-D conformal heating capabilities in ex vivo tissue and compare to theoretical predictions. Devices were fabricated with 1-3 transducers at 6.5-8 MHz with sectors from 90-180deg and heating length from 15-35 mm housed within a 6 mm diameter water-cooled PET catheter. Directional heating from sectored transducers can extend lateral penetration of therapeutic heating (41degC) > 2 cm while maintaining rectum and bladder temperatures within 12 mm below thermal damage thresholds. MR artifacts extended <2 mm beyond the device and real time thermal imaging was used to guide power selection to shape heating profiles in axial and coronal slices. Endocavitary delivery of ultrasound thermal therapy is feasible and 3-D conformal capabilities will benefit targeted cervical hyperthermia.